A common and well known form of harvesting machine is a rotary combine. Rotary combines are available in various designs and models to perform the basic functions of harvesting, threshing, and cleaning of agricultural crop such as grain. As used herein, the term "grain" is meant to include corn, wheat, rye, oats, barley, flax seed, sorghum, soy beans, mixed grain, and any other food grains, feed grains, and oil seeds.
A typical combine includes a crop harvesting apparatus which reaps planted agricultural crop as the combine is driven across a field. A feeder mechanism arranged at the forward end of the combine operates in combination with the harvesting apparatus and feeds the harvested crop to a threshing apparatus arranged within a housing of the combine. The threshing apparatus separates the harvested crop into grain and material other than grain.
While the threshing apparatus acts to separate a substantial portion of the crop or grain from material other than grain, chaff and/or straw remains intermixed with the grain, and a further cleaning or separating action is normally required. Further separation is normally achieved in a cleaning section of the combine.
The cleaning section of a conventional combine is located to receive threshed materials including chaff, grain and other material expelled from the threshing apparatus. A typical cleaning section includes two sieves vertically arranged one above the other and a fan which produces a flow of air directed through the sieves. Reciprocation of the sieves facilitates arrangement of the threshed materials into a crop layer or mat on top of the sieves.
Separation of the grain from residue materials other than grain is facilitated by the air from the fan flowing upwardly through the sieves. The upwardly directed air creates a force which urges relatively light residue material including straw, chaff, and the like to float on top of the sieve and into an airborne state such that it may be directed toward and expelled from a discharge end of the combine. Heavier seeds or clean grain tend to move to the sieve and fall through a series of openings or passages into a clean grain collector.
Threshed materials passing to the uppermost sieve of the combine forms a conglomerate mass of grain and material other than grain which is difficult to separate and clean. As will be appreciated, the chaff acts to clog the sieve and, thereby, retard and sometimes inhibit clean grain from passing therethrough. As is evident from the prior art, considerable effort regarding fan design has been done over the years to produce an efficient flow of air which is necessary to provide a proper cleaning action for the threshed crop material.
The upper sieve of the cleaning section is designated a chaffer sieve, and the lower sieve is designated a grain sieve. The purpose of the chaffer sieve is to separate heavier grain particles from lighter chaff, straw, and other residue materials. The chaffer sieve also effects some sorting of materials received thereon by size. The purpose of the grain sieve is to provide a secondary cleaning action thereby inhibiting contamination of the grain passing into the clean grain collection. As will be appreciated, passing grain through two separate sieves during a cleaning process is a limiting factor which adversely effects combine capacity and productivity.
There are basically two separate and distinct sieve designs. One design proposes configuring the chaffer sieve as an air foil which provides a series of adjacent apertures of a fixed size over a grain cleaning area of the sieve. An air foil advantageously allows the majority of air presented to an undersurface thereof to flow therethrough. In high rate harvesting conditions, however, the fixed size of the air foil apertures lacks the ability to separate grain from material other than grain. Consequently, a large portion or percentage of threshed material including grain is passed over the discharge end of the air foil and is lost to the ground thereby adversely effecting combine productivity.
Another sieve design involves a series of angularly adjustable louvers or slats which define open passages between confronting surfaces of adjacent louvers. The angular adjustability of the louvers allows the size of the opening or passage between louvers to be changed or adjusted. The air flow through the passages defined between the louvers is less than an air foil design. Moreover, the laterally elongated openings between confronting surfaces of adjacent louvers allows elongated materials, such as straw and the like, to pass therebetween. Successful operation of a louver-type sieve relies in large part on the proper opening between louvers. If these openings are too small for the particular material being harvested, there is naturally a significant increase in the thickness of the layer of materials on the sieve, and thus, the effectiveness of the fan is diminished. If the openings or passages between the louvers of the sieve are too large, material other than grain passes through the sieve. Carefully regulated control of the openings is difficult to achieve and, furthermore, consumes valuable time which is at a premium during a harvesting operation.
Thus, there is a need and a desire for a sieve which provides a beneficial flow of air therethrough and yet limits the amount of grain passing from a discharge end thereof.